Special Issue; Products for Industrial Machinery - NTN

More documents

Recommendations

Info

NTN TECHNICAL REVIEW No.742006 The results of bearing temperature measurements with the constant pressure preloading system are graphically plotted in Fig. 10(a), and the results with the definite pressure preloading system are provided in Fig. 10(b). With the definite preloading system that keeps the axial load to the bearings at a near-constant level, the test rig was run at dmn of 2 million (15000 min -1 ). As a result, the authors confirmed that the Temperature ˚C Temperature ˚C 60 50 40 30 20 10 60 50 40 30 20 10 Table. 3 Temperature rise test conditions Item Details Grease chamber technical data Bearing preloading Shouldered surface clearance Prefilled grease in bearing Heat cycle Constant pressure preloading test Definite position preloading test 0.08 mm 47 g Grease-A prefilled None 2.2 kN Clearance after mounting 0 Jacket cooling oil temperature Room temperature ±1˚C Inner ring temperature Outer ring temperature 0 0 4000 8000 12000 16000 Running speed of inner ring min -1 (a) Constant pressure preloading Inner ring temperature Outer ring temperature 0 0 4000 8000 12000 16000 Running speed of inner ring min -1 (b) Definite position preloading Fig. 10 Temperature rise versus rotational speed temperature on the bearings at various running speeds were stable and the spindle can operate without any problems. At the same time, as can be understood from Fig. 10, with the definite position preloading system, the temperatures on the inner ring and outer ring at dmn of 1.8 million (14000 min -1 ) were 46˚C and 37˚C, respectively, which are roughly the same as in the case of the constant pressure preloading system that runs at the same speed. However, with the definite position preloading system at dmn of 2 million (15000 min -1 ), the temperatures on the inner ring and outer ring were 53˚C and 43˚C, respectively. These values are higher than those of the constant pressure preloading system. Since the running bearings were overloaded (preloading) under this situation, the authors judged that the bearings were not capable of operating normally under these conditions. Assuming that the limiting speed at a particular bearing temperature in the definite position preloading system is the same as the bearing speed of the same bearing with the constant pressure preloading system, and based on the test result described above, the limiting speed of the definite preloading system matches dmn of 1.8 million (14000 min -1 ). Thus, by using the authors’ new grease lubrication system, it is possible to operate machine tool spindles at higher speed ranges than had been previously possible with air-oil lubrication systems. 4.2 Endurance test The durability of bearings lubricated with the authors’ new grease lubrication system was evaluated. Durability tests were performed with both a definite position preloading system and a constant pressure preloading system. The test rigs used are illustrated in Figs. 9(a) and 9(b). The constitution of the grease chamber and the operating conditions used are summarized in Table 4. The bearing speed of both the constant pressure preloading system and the definite position preloading system were at dmn of 2 million (15000 min -1 ) to emphasize the running speed. With the definite position preloading system, overloading would occur as judged from the results obtained in the previous Sec. 4.1. Therefore, the initial clearance of the bearing was adjusted so that an appropriate preload (axial load 2.2 kN) was attained at the speed of 2 million dmn (15000 min -1 ). In the adopted heat cycle pattern, as illustrated in Fig. 11(a), each repeated cycle consists of 50 hours of operation and 1 hour of rest. The temperature difference in each cycle was approximately 15˚C. With the definite position preloading system, the spindle was also tested in both vertical and horizontal positions to -14-
Development of a New Grease Lubrication System for Machine Tool Main Spindles examine the effect of the attitude of the main spindle on the bearing life. The test results are graphically illustrated in Fig. 11(b). The endurance test results of bearings lubricated with the authors’ new grease lubrication system are presented along with the results for a conventional grease lubricated angular contact ball bearing with seals on both sides that was tested under the same conditions. When operated at dmn of 2 million, the conventional grease lubricated bearing seized after approximately 500 hours had elapsed. It is clear that the authors’ new grease lubrication system is effective at providing a sufficient amount of lubricant and an uninterrupted lubricant supply. A certain bearing lubricated with the authors’ new Item Grease chamber technical data Operating conditions Definite position preloading Constant pressure preloading Table. 4 Endurance test conditions Details Shouldered surface clearance 0.08 mm Prefilled grease in bearing Grease-A Amount of prefilled grease 47 g Spindle attitude and number of spindles tested Vertical (2 units), horizontal (1 unit) Initial clearance that coincides with Preload 2.2 kN axial load when the bearing is running at dmn 2 million Running speed dmn 2 million Spindle attitude and number of spindles tested Preload Running speed Jacket cooling oil temperature Horizontal (1 unit) 2.2 kN dmn 2 million Room temperature ±1˚C lubrication system has successfully achieved 18000 hours of continuous operation and is still running. Incidentally, the endurance test results reported here are all obtained from bearings lubricated with Grease-A. Currently, a bearing endurance test is in progress with the definite position preloading system using Grease-B. The bearings being tested in both horizontal and vertical attitudes have already achieved 2000 operating hours and are still operating smoothly. 5. Conclusion To cope with the mounting needs for higher-speed machine tool main spindles, the authors have developed a unique grease lubrication system that allows the bearings being lubricated to be completely maintenance-free. By using this lubrication system that features heat cycle-driven base oil delivery from the grease chamber, an angular contact ball bearing with a 100 mm bore diameter can run at dmn of 1.8 million with a definite position preloading system and at dmn of 2 million with a constant pressure preloading system. In summary, the authors’ new grease lubrication system is a unique lubrication scheme that helps achieve better machine tool performance and mitigate environmental impacts because it possesses a completely maintenance-free operation of the grease lubrication system and is also capable of higher speed operation not possible with any conventional grease lubrication system. Temperature 41˚C 26˚C 1h References 1) NTN Precision Rolling Bearings, Cat. No. 2260/E 2) Y. Akamatsu, M. Mori: Development of Eco-friendly Oil Jet Lubricated Angular Contact Ball Bearings for Machine Tool, NTN Technical Review No. 72 (2004) pp. 6-10. 50h 50h (a) Time h Heat cycle pattern New grease lubrication Conventional grease lubrication Constant pressure Definite position Definite position Definite position Definite position Definite position Horizontal Vertical Vertical Vertical -15- Horizontal Horizontal Continuous operating time h 0 5000 10000 15000 20000 25000 30000 Seizure Photos of authors (b) Bearing endurance of new and conventional grease lubrication system Fig. 11 Endurance test results Sun-Woo LEE Elemental Technological R&D Center Masatsugu MORI Elemental Technological R&D Center
Page 1 and 2: 88th Anniversary Special Issue; Pro
Page 3 and 4: R No.74 TECHNICAL REVIEW Special Is
Page 5 and 6: NTN TECHNICAL REVIEW No.742006 Pref
Page 7 and 8: Trends in Recent Machine Tool Techn
Page 13 and 14: Development of a New Grease Lubrica
Page 15 and 16: Development of a New Grease Lubrica
Page 17: Development of a New Grease Lubrica
Page 21 and 22: High-Speed Tapered Roller Bearing f
Page 29 and 30: Minimum Quantity and Cooling Jet Lu
Page 31 and 32: Minimum Quantity and Cooling Jet Lu
Page 33 and 34: dmn17010 4 Sealed High-speed Angula
Page 39 and 40: Development of Aerostatic Bearing S
Page 41 and 42: Development of Aerostatic Bearing S
Page 43 and 44: Introduction of New Products for Ma
Page 49 and 50: Atmospheric Control Method for JIS-
Page 59 and 60: The Influence of Hydrogen on Tensio
Page 67 and 68: Technical Trends in Bearings for Of
Page 69 and 70:
Technical Trends in Bearings for Of
Page 71 and 72:
Technical Trends in Bearings for Of
Page 73 and 74:
Unit Products for Office Equipment
Page 75 and 76:
Unit Products for Office Equipment
Page 77 and 78:
-73- Unit Products for Office Equip
Page 79 and 80:
Honing Sludge and Electro Furnace D
Page 81 and 82:
Page 83 and 84:
Page 85 and 86:
Ultra-Clean Bearing for Clean Envir
Page 87 and 88:
Ultra-Clean Bearing for Clean Envir
Page 89 and 90:
Development of New RCT Bearing for
Page 91 and 92:
Page 93 and 94:
Page 95 and 96:
High Load Capacity Cylindrical Roll
Page 97 and 98:
Page 99 and 100:
Page 101 and 102:
The Rust Guard Bearings of Highly C
Page 103 and 104:
The Rust Guard Bearings of Highly C
Page 105 and 106:
“SSB” of Sliding Aseismic Isolu
Page 107 and 108:
“SSB” of Sliding Aseismic Isolu
Page 109 and 110:
Monodrive Two-Way Feeder Flow direc
Page 111 and 112:
Monodrive Two-Way Feeder MD20: 17.5
Page 113 and 114:
"Hybrid Bearphite" a Sintered Metal
Page 115 and 116:
Page 117 and 118:
Page 119 and 120:
Page 121 and 122:
New Products Information PTJ High-A
Page 123 and 124:
New Products Information Ultra-Low
Page 125 and 126:
New Products Information Hub Bearin
Page 127 and 128:
New Products Information Low-Emissi
Page 129 and 130:
New Products Information Advanced F
Page 131:
NTN TECHNICAL REVIEW No.74 Printed
show all

Special Issue; Products for Industrial Machinery - NTN

Create successful ePaper yourself

Delete template?

Save as template?